The glycosphingolipids of meconium of a human O Le(a--b+) secretor have been subjected to structural and immunological characterization. Mass spectrometry, proton NMR spectroscopy, and gas-liquid chromatography were used for chemical analyses, and haemagglutination-inhibition for immunological characterization. The great amounts of glycolipids present also facilitated the analyses of minor species constituting only 1% or less of the total weight of the non-acid glycolipids. Glucosylceramide and galactosylceramide were the dominating glycolipids comprising 15 and 30%, respectively, of the total weight. The diglycosylceramides found were lactosylceramide and digalactosylceramide. The globo series was represented by globotriaosylceramide, small amounts of globotetraosylceramide, part of which had ceramide of phytosphingosine and hydroxy fatty acid, and a minor species of monofucosyl hexaglycosylceramide with an inner globotetraose oligosaccharide. No Forssman or Forssman-like antigen was found. The lacto series, quantitatively approximately 30% of the total weight, was mainly represented by lactotetraosylceramide and H-active, Lea-active, and Leb-active glycolipids with 5-6 sugars based on lactotetraosylceramide. Minor species having 0-3 fucoses in their carbohydrate chains and carrying up to 11 sugar residues were also identified. Great amounts of free ceramides were also found to be typical for this tissue.